It is well established in the prior art that absorbable fibers suitable for constructing biomedical constructs with prolonged strength retention profile, as in certain surgical sutures and meshes as well as prosthetic tendons and ligaments, need to be based on polymers having (1) high molecular weight; (2) a high degree of crystallinity; and (3) minimum or no monomeric species. These requirements were claimed to have been fulfilled by the l-lactide/glycolide copolymers described in U.S. Pat. No. 5,425,984 and EP Application No. 241,252 (1987). However, in certain high load-bearing applications where a prosthetic fibrous construct experiences cyclic stresses and is expected to maintain a substantial fraction of its initial strength for several weeks post-operatively, additional requirements are imposed. Typical examples of such constructs are surgical meshes for hernia repair and prosthetic tendons and ligaments. These additional requirements are expected to be associated with having a high degree of toughness, as measured in terms of the work required to break, without compromising, significantly, their high tensile strength, high elastic modulus, low stretchability, and high yield strength. Such requirements also are expected to be associated with a polymeric chain with higher hydrolytic stability than those containing glycolate sequences are. Unfortunately, the prior art of absorbable polymers provides conflicting teachings that may be applied towards meeting the aforementioned additional requirements. To increase toughness, the introduction of more flexible ε-caprolactone-based sequences in polyglycolide chain has been used successfully in the production of low modulus sutures (see, for example, U.S. Pat. Nos. 4,605,730 and 4,700,704) but with compromised strength. A similar situation is encountered in the copolymer of glycolide and trimethylene carbonate (see, for example, U.S. Pat. No. 4,429,980). Interestingly, fibers made of these two types of copolymers do display a lower propensity to hydrolysis than polyglycolide, but their strength loss profiles remain unsuitable for long-term, load-bearing applications.
Substantial developments in the field of tissue engineering were made possible by the availability of absorbable polymers and their use as a scaffold for cell attachment and growth in three-dimensions. However, almost all of the applications of absorbable polymers in tissue engineering were based on polyglycolide or high glycolide copolymers, which lose their mechanical integrity within four weeks. Meanwhile, the new trends in tissue engineering research rely on implanting the absorbable scaffold at biological sites that require the retention of their mechanical integrity well over a period of four weeks. Such contemporary requirements and consistent call for substrates that encourage cell attachment as well as being biomechanically compatible with active cells provided an incentive to explore the feasibility of designing absorbable chain molecules with the aforementioned requirements and other desirable features for their use in tissue engineering applications. And this invention deals with the synthesis of segmented, high lactide, absorbable copolymers which can be easily converted to textile constructs for use as scaffolds for tissue ingrowth having (1) a strength retention profile that allows the retention of their mechanical properties well beyond the four-week limit of presently used synthetic absorbables; (2) an absorbable surface coating that is compliant and carries a positive charge which encourages cell attachment; and (3) a discernable fraction of very low Tg, compliant segments that dominate the fiber surface and hence, provide a biomechanically compatible substrate for actively growing cells.